Internet webpage rerouting and lag

I don't know why, but lately my computer has lagged whenever it feels like when I'm using firefox and It's by pure luck if I watch a youtube video now without having to shut down firefox through it's process through task manager. I have Window's live onecare, and I scanned, but it only found a trojan/password stealer (Who knows how THAT got there...??) and nothing else. The internet webpage rerouting doesn't happen often, but there are times where I search something in google, and when I click a link, it just goes wherever it wants, or sometimes I'm in a site and clicking a link and it goes wherever it wants. And bothering to download anything on firefox is just asking for me to pull the plug on my computer so I can restart it because task manager probably won't come up anytime soon.

I tried system restore as well to 2 weeks prior, and it still lags and all.

I don't know if the 8 steps fixed it because I THINK my computer is working fine now, but I thought that before too and it just fell apart again.

Any help would be nice =)

EDIT: Yeah, it's still laggy. And might I add that the lag isn't confined only to firefox, with firefox not running (usually after I closed it though) the lag remains.

Please guys, I hate to sound pushy, but I can barely do anything without it lagging..

EDIT: Amd I've noticed that when streaming anything, the commit charge in task manager increases ridiculously where it gets to the point that it goes over a thousand and it starts lagging when before I began streaming it was only 4xx.